Field of the Invention
The present invention relates to a process for preparing a cathode active material for a lithium secondary battery. More particularly, it relates to a process for preparing a cathode active material for providing lithium secondary batteries which has excellent packing properties and provides a lithium secondary battery having a high capacity and satisfactory high-temperature characteristics and preferred as a driving power source.
With the recent rapid development of portable and wireless electronic equipment such as personal computers and telephones, the demand for secondary batteries as a driving power source has been increasing. In particular lithium secondary batteries are expected for their smallest size and high energy density. Cathode active materials for lithium secondary batteries meeting the demand include lithium cobaltate (LiCoO.sub.2), lithium nickelate (LiNiO.sub.2), and lithium manganate (LiMn.sub.2 O.sub.4). Having an electrode potential of 4 V or higher with respect to lithium, these lithium complex oxides provide lithium secondary batteries having a high energy density.
Compared with LiNiO.sub.2 and LiCoO.sub.2 having a theoretical capacity of about 280 mAh/g, Li.sub.2 O.sub.4 has a theoretical capacity as low as 148 mAh/g but is deemed suited for use in electric vehicles because of an abundant and inexpensive supply of manganese oxide as a raw material and freedom from such thermal instability in charging as observed with LiNiO.sub.2.
There is a problem that lithium secondary batteries using these Li-Mn complex oxides as a cathode active material are inferior in high-temperature characteristics to those using conventional LiCoO.sub.2 or LiNiO.sub.2 as a cathode active material.
Displacement of part of manganese with lithium or a transition element has been attempted as a countermeasure, which brings about improvement to some extent but is still insufficient.
The problem of the small battery capacity is also outstanding.